Generally the present invention relates to the cooling of the rotor trochoidal rotary internal combustion engines of the spark ignition and compression ignition types.
Rotary piston engines to which the present invention relates have a multi-lobed piston member (hereinafter referred to as a "rotor") rotatably mounted on a crankpin of a crankshaft, with the crankshaft rotatably mounted in a housing. The multi-lobed rotor has the shape of a trochoid or of a curve inside and parallel to a trochoid, while the housing has an inner surface shape corresponding respectively to the outer enclosing curve, or outer envelope, of the trochoid or of the inside parallel curve; these alternatives hereinafter being encompassed by reference to "trochoid" or the "outer enclosing curve, or envelope" thereof. Rotational phasing of the rotor relative to the shaft and the housing is ensured by an external gear which is fixed to the rotor and which meshes with an internal gear fixed to the housing. The trochoid has at least two lobes and theoretically it can have any greater number of lobes. The number of lobes determines the gear ratio required for phasing and also the number of working chambers in the housing; the number of such chambers being equal to the number of lobes plus one. Thus a family of trochoidal piston rotary engines exists. The present invention is particularly relevant to two lobe trochoid rotary piston engines with three working chambers, and the following description largely is directed to engines which have a single two lobe, trochoid shaped rotor. However, the invention extends to engines having more than one rotor and to engines having at least one rotor with three or more lobes.
It is known that rotors of a rotary engine require cooling to dissipate heat absorbed during the combustion process. In addition rotors are also subjected to mechanical stresses particularly during combustion, and it is essential that distortion of the rotor peripheral and side surfaces is kept to a minimum to avoid loss of gas pressure and thus performance.
Although the prior art, such as illustrated by U.S. Pat. No. 3,131,379 and 3,266,468 to Pears, recognises the need for rotor cooling by oil or water, the proposed large channels and thin walled rotor construction fail to allow for the distorting forces produced during combustion. For high speed engines where there is a need for a lightweight rotor generally made from materials such as an aluminium or magnesium alloy or graphite, the construction as suggested by the cited marks would not be suitable or possible. For these materials the rotor needs to be substantially solid if distortions are to be kept to acceptable levels and maintain sealing integrity between the rotor surface and apex seals, and between the compression side seals and engine side plates. We have confirmed this requirement by extensive computer analysis and testing.
It is an objective of this invention to provide a rotor better adapted to provide for oil cooling of the rotor.